Hi there! It sounds like you're experiencing a bit odd behavior with Nicegram where everything turns black and white upon logging in with your mobile number. Let’s dive into that together and see what we can do to resolve it!

1. Check Display Settings: Sometimes, the display settings on your device might affect how colors are shown. Go to your device's settings and look for "Display" or "Color Mode." Make sure no options for "Grayscale," "Night Mode," or similar are enabled.

2. Restart the App: Close Nicegram completely and then reopen it. Sometimes a simple restart can help refresh any temporary glitches.

3. Clear App Cache: If you're using a browser to access Nicegram, try clearing your browser's cache. You can do this by going into your WebKit settings under "Privacy" or "Data Management" and clearing the cache.

4. Reinstall Care: If those steps don’t work, consider logging out and reinstalling the Nicegram app. This process can often solve many display-related issues.

If these steps don't help, I could look for more specific solutions for display issues related to Nicegram. Would you want me to do that?